1. Field of the Invention
This invention relates to acrylate hydrosols and to a process for the production of hydrosols based on acrylates using .alpha.-sulfocarboxylic acid esters.
2. Statement of the Related Art
Hydrosols are polymer dispersions having a particularly small particle size of about 0.08 .mu.m and smaller.
Acrylate-based hydrosols have been known for some time. They are used mainly in the coating field as primers for impregnating porous substrates (J. L. Mondt, J. Oil Col. Assoc. 60, 398 (1977) and H. P. Beardsley, R. N. J. Selby, Paint Technol. 40, 263 (1968)).
The production of pure acrylate hydrosols is described in British Pat. Nos. 1,114,133 and 1,109,656. However, the emulsion polymers described there, which are produced with corn starch or fatty alcohol sulfate as emulsifier, have to be blended with a comminution agent (of which the function is not defined) to obtain the necessary hydrosol particle fineness.
For producing hydrosols of the above type, it has already been proposed to use a combination of fatty alcohol sulfates with fatty alcohol and/or alkyl phenol ether sulfates as emulsifier. Although hydrosols produced in this way are stable and suitable for certain applications, their viscosity increases rapidly if their solids content is adjusted to more than 40% by weight. However, particularly thin-flowing products of relatively high concentration are required for applications in the coating field.
.alpha.-sulfocarboxylic acids are already known as polymerization emulsifiers, but their use in the producton of hydrosols is unknown. Descriptions of the use of .alpha.-sulfocarboxylic acids in emulsion polymerization will be found in:
______________________________________ German patent corresponding English language application patent or patent application ______________________________________ 17 20 430 none (Derwent Abstract) 17 70 217 -- 17 70 223 -- 19 01 493 U.S. 3,732,178, G.B. 1,287,361 19 01 495 none 19 18 414 U.S. 3,732,178 19 19 705 none 20 15 660 U.S. 3,836,497 20 54 103 G.B. 1,358,429 33 39 407 -- -- G.B. 745,927 -- U.S. 2.694,052 ______________________________________
The production of .alpha.-sulfocarboxylic acid esters is described in German patent application 11 86 051 in German Pat. No. 1,248,645 and in British patent application 2,089,793 (as well as corresponding German patent application 30 47 897). Finally, a process for the production of .alpha.-sulfo fatty acid salts is described in U.S. Pat. No. 4,021,460 (and corresponding German patent application 25 44 846), according to which from 0.5 to 10% by weight of an inorganic sulfate in the form of a powder free from water of crystallization is added to a mixture of 100 parts by weight of an alkyl ester of a saturated fatty acid containing a C.sub.8-22 -fatty acid function and a C.sub.1-6 -alcohol function, followed by the addition of from 1 to 2 mols per mol of fatty acid ester of gaseous SO.sub.3 in admixture with an inert gas at temperatures of up to at most 100.degree. C. Salts of .alpha.-sulfo-fatty acid esters which may be made up in the form of highly concentrated solutions in water and which contain at most small equantities of free acids may be obtained by the process according to U.S. Pat. No. 4,404,143 (and corresponding German patent application 31 23 681) which describes the post esterification of the sulfonated product by the addition of an alcohol before neutralization.
The production of .alpha.-sulfocarboxylic acids is described in U.S. Pat. No. 2,460,968, according to which aliphatic acids containing at least 6 C-atoms are sulfonated with chlorosulfonic acid in a solvent, the chlorosulfonic acid being used in a slight excess and the gases formed (HCl) and the solvent being subsequently removed by the distillation.